Method of and apparatus for burning low heat content fuel



Oct. 1, 1963 R. M. HARDGROVE METHOD OF AND APPARATUS FOR BURNING Low HEAT CONTENT FUEL 2 Sheets-Sheet 1 Filed April 7, 1954 INVENTOR V R44 p. 1 M. {fa/9062042- m T w a 0 x 5 J Z In l||||| n \J m n ,4, :1 1| 3 :hllv. n- 6. 4 i H 2 J i 4 M H IHHHHHHH H H MMNE w rma. N. fi. "a

Oct. 1, 1963 R. M. HARDGROVE 3,105,540

METHOD OF AND APPARATUS FOR BURNING LOW HEAT CONTENT FUEL 7 Filed Apnl 7, 1954 2 Sheets-Sheet 2 Tl I I I I I!" i l f i l i J Q INVENTOR x Pup/ l M Ha ue/7am;

ATTORNEY United States Patent rad 3,105,540 METHGD AND APPARATUS F63 BURNENG LGW FEAT CG TENT FUEL Ralph M. Hardgrove, North Canton, Shin, assignor to The Bahcoci; & Wilcox Qcmpany, New York, N.l.,

a corporation of New Jersey Filed Apr. 7, 1954, Ser. No. 421,656 8 (til. 158-1) The present invention relates to the combustion of fuel, and more particularly to a method of burning a low heat content fuel.

The combustion of gases containing small amounts of combustible matter has proven difiicult in the past. Many of these low heat content gases do not contain sufhcient combustible matter for self-sustaining combustion, and have heretofore been burned in combination with high heat content fuels whereby the combustion zone for the combined fuels was maintained at a sufficient temperature to burn the combustible content of the low heat content fuel. in burning such fuels in combination, it is highly desirable to substantially complete the combustion of the high heat content fuel before mixing the hot products of combustion with the low heat content fuel to ignite and burn the latter. Complete combustion of both fuels can be accomplished, however, by burning the high heat content fuel in a separate zone in radiant heat exchange relation with a mass of the low heat content fuel. The low heat value fuel is partially heated by'radiant heat and is further heated by intimate mixing with the hot gaseous products of combustion from the high heat value fuel. The low heat value fuel burns when the temperature thereof attains the ignition temperature depending upon the composition of the fuel and the availability of 0:0 gen. The mixing of the hot gases also mixes free oxygen with the combustibles for complete combustion.

In the present invention an upright cylindrical furnace of refractory material is provided with a plurality of vertically spaced, horizontally arranged rows of burners for the admission of a high heat value fuel to the furnace. Each row of burners is arranged with the burners circumferentially equally spaced about the furnace to discharge streams of fuel and air thereto in a horizontal direction radial or non-radial with respect to the vertical axis of the furnace. Rows of ports are also provided in the wall of the furnace for the admission of the low heat content fuel. Each row of ports is disposed horizontally of the furnace and vertically spaced below an adjacent row of high heat content fuel burners. The ports in each row are horizontally spaced between the vertical positions of the upwardly adjacent burners so as to form a staggered relationship between the position of the burners and ports in the furnace wall. The low heat value fuel is introduced into the furnace in a horizontal direction non-radial with respect to the axis of the furnace. Both fuels follow a helical direction of movement through the furnace, resulting in intimate mixing between the gases of combustion and the different fuel streams. The hot products of combustion from both fuels discharge in an upward direction from the cylindrical fur-nace'into a vapor generator for the production of vapor and conversion of the heat in the gases to a more useful form of energy.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in wlr'ch I have illustrated and described an embodiment of my invention.

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Of the drawings:

FIG. 1 is an elevation of a furnace, in section, constructed in accordance with the present invention, as combined with a vapor generating unit; and

MG. 2 is a plan vicw'of the apparatus taken on the line 2 2 of Fl". 1.

in the illustrated embodiment of the invention, a low heat content gas formed during the regeneration of a catalyst used in a h drocarbon cracking unit is burned in an upwardly elongated cylindrical furnace 10. The gas from the regenerator kiln is largely composed of a mixture of CO CO and N with a small amount of oxygen and water vapor, and with a small amount of hydrocarbon vapors. The CO and hydrocarbon can be burned to CO with the evolution of heat, and while the heat value of the gas per unit of weight is quite low, the gas is available in large volumes and the total available heat therein is well worth recovering for the generation of steam for power or process purposes. This gas cannot be ignited and burned under self-sustaining combustion conditions, but if maintained at a temperature of approximately 150G F. it can be burned. As shown in the drawings, fuel oil is also burned in the cylindrical furnace to raise the temperature of the gas to an ignition and self-sustaining combustion temperature. As hereinafter described, the low heat gas and high heat fuel oil or gas is separately introduced into the furnace and in a preferred manner for efiicient release of the heat in both fuels. Thereafter the products of combustion are passed over a plurality of hea t absorbing surfaces for the generation of steam.

Referring to PEG. 1, the furnace 19 is of circular horizontal section havin: an upright cylindrical ceramic refractory wall ll which extends upwardly from a substantially fiat bottom 12 to a frusto-conical collar 13. The frusto-conical collar merges into a cylindrical wall 14 of reduced diameter opening upwardly to the lower portion of an associated vapor generator 15.

The vapor generator 15 is shown as being of the twodrum type with the upper drum 16 connected with the lower drum l7 by vapor generating tubes which are arranged in a plurality of generally upright banks 2t 21 and 22. A chamber 23 is positioned forwardly of the tube bank 2% with the roof 24, front wall 25 and side walls 26 of the chamber provided with closely spaced vapor generating tubes connected into the circulatory system of the vapor generator. The side wall tubes 27 are substantially upright and are connected with upper and lower headers and 31, respectively, while the roof and front Wall tubes 32 connect at their upper ends with the drum to and at their lower ends with a horizontally disposed header 33. A double row of screen tubes 34 are located between the chamber 23 and the tube bank 2% in the path of gas flow from the chamber 23 to the banks 29, 21 and 22 of the vapor generator. The screen tubes are connected at their upper ends with the drum and their lower ends open to a transverse header 35. The bottom of the chamber 23 is open and fitted to the collar 14 of the furnace if), so that the hot gaseous products of combustion generated in the furnace flow upwardly into the chamber 23, turn through an angle of to. pass through the tube banks 2d, 2d and 22, and leave the vapor generator through a flue gas outlet 36 rearwardly of the tube bank 22.

The low heat value gas from the catalyst regenerating kiln passes at a superatmtospheric pressure through a duct to the vicinity of the furnace 1G Where the gas is divided to pass through a pair of .ducts to (only one shown) to opposite sides of the furnace. Thereafter, the gas stream is again divided for substantially equal distribution to upright manifolds for delivery to the gas inlet ports positioned in the wall of the furnace. The gas delivered to the duct system is supplied at a temperature of approximately 8ll0l000 F. and a pressure of approximately 2 pounds per square inch gage (p.s.i.g.) Under these conditions, the ducts are lined with suitable heat insulating material.

As shown particularly in FIG. 2, the duct it; is disposed horizontally at a level approximating the position of the collar 13, with one manifold 4-1 connected directly therewith and a second manifold 42 connected with the duct 40 by a duct extension 4 3. The branch duct 44 on the opposite side of the furnace 19 (see FIG. 1) corresponds in general with the duct 43, and is connected with the upright manifold 4-5. In the embodiment shown, the four manifolds are equally spaced circumferentially of and equally radially spaced from the vertical axis of the furnace. Each manifold is provided with three vertically spaced horizontally disposed off-take pipes 5 opening to the furnace through an individual port 51 in the fun nace wall. Each off-take pipe 5b is provided with a damper 52 for individual regulation of gas flow to its connected port.

As shown in FIG. 1, the gas ports 51 are disposed in rows of four in the wall ill, with the rows A, B and C vertically spaced between the lower and the upper intermediate portions of the furnace it The off-fake pipes 50 of the port row C are shown in FIG. 2 wherein it will be noted each stream of low heat value gas projected through each port is directed horizontally with tangential and radial components of movement with respect to the vertical axis of the furnace.

An extension of the axial centerline of each of the offtake pipes St in each of the rows A, B and C is tangent to an imaginary circle located intermediate the vertical axis and the internal surface of the furnace wall. With the arrangement described, three vertically spaced horizontal zones are formed in which the initially projected streams of gas rotate in a counterclockwise direction, when view from the upper end of the furnace 1G.

Since the low heat value gas of the illustrated embodiment of the invention has a heat value of the order of to B.t.u. per cubic foot, it is necessary to provide a temperature of 14-00-1500 F. for the ignition of the combustible constituents therein. The necessary furnace temperatures are attained by the combustion of a high heat value fuel, such as fuel oil.

As shown, the fuel oil is introduced into the furnace through a plurality of fuel oil burners 53 which are arranged in vertically spaced rows D, E and F with four burners in each row. The burners are equally spaced circumferentially of the furnace in each row, with each fuel oil burner spaced between the individual gas inlet ports 51, and with each row of fuel oil burners spaced above an adjacent row of gas inlet ports. In the embodiment of the invention there are 12 gas inlet ports 51 arranged in three rows of four ports in each row. An equal number of fuel oil burners 52 are provided, so that the vertical and horizontal arrangement of both ports and burners is staggered.

Referring particularly to FIG. 2, the row F of oil burners is shown as arranged with an extension of each of the axial centerlines, lying in a horizontal plane and projecting inwardly of the furnace it) to intersect an imaginary circle concentric with the vertical axis of the furnace. The direction of the entering fuel oil stream is such as to provide a counterclockwise direction of movement within the furnace, as viewed from the collar 13.

When burning the gas obtained from the regeneration of the catalyst used in a hydrocarbon conversion process, there may be sufficient oxygen in the gas to burn the CO to CO under suitable furnace temperature conditions. The combustion air for the fuel oil and any excess air required for combustion of CO gas is delivered to the furnace It) with the fuel oil through registers 5 associated with each oil burner 53. A burner and airwregister of this general type is disclosed in the C. E. Lucke Patent 2,242,797.

The combustion air for the fuel oil and the excess required for CO gas is supplied by a forced draft fan (not shoe n) which delivers the air at a superatrnospheric pressure to an air plenum chamber 55 positioned beneath the bottom 12 of the furnace. The chamber is enclosed by metallic walls $6 forming an octagonal outer wall, with each flat side surface of the octagonal chamber provided with an air out et 57 which distributes the cornbustion air substantially uniformly beneath the bottom 1.2 of the furnace. Part of the structural support from the bottom 12 of the furnace includes radial steel web memers which extend outwardly from the corners of the octagonal plenum chamber walls to the outer circumference of the wall ll. The web members have a flat upper edge and a lower edge which tape-rs toward the outside of the furnace. Thus the combustion air passing through the outlets 57 of the chamber 55 is in communication with the entire lower surface of the furnace bottom so that air from each of the outlets 57 can pass to each of the air openings at leading to four vertically extending ducts 61 connected with the three vertically aligned air registers 54. Two of the vertically extending air ducts are shown in FIG. 1, while the top of the ducts and the uppermost register 54 of two of the ducts is shown in section in FIG. 2.

The oil burners 53 are shown as being of a well known mechanical atomizing type, although it will be understood steam atomizing oil burners can be utilized, if desired. it will further be understood that other high heat value fuels, such as natural gas or the like canbe substituted for the fuel oil shown and described.

In the operation of the apparatus described, the fuel oil is burned with low excess air in zones which are each upwardly adjacent a zone of CO gas introduction. While the gases in each of the zones mingle to some extent immediately after introduction of the fuel into the furnace, the fuel oil does not mingle with the CO gas to any appreciable extent until the fuel oil combustion is substantially complete. This is accomplished by the use of high velocities in the initial introduction of the CO gas to the furnace, such as for example, velocities in excess of 10,000 feet per minute. correspondingly, the fuel oil is finely atomized and intimately mixed with combustion air to attain quick combustion. The combustion of the fuel oil heats the CO gas by radiation and by convection as the combined gases are intimately mixed in their swirl ing upward movement toward the collar 14. The restriction imposed by the frusto-conical member 13 further causes an increased mixing of the mingled gases so that the combustibles remaining in the gases are finally con sumed in the chamber 23. Normally, any combustion occurring in the chamber 23 will be minor.

The products of combustion will be at a'temperature surlicient to generate steam in passing through the chamber 23 and the banks 2%, 2i and 22 of the vapor generator. Even though the heat content of the gas obtained in the regeneration of a catalyst is low, per unit of gas weight, the B.t.u. content in the gas can be effectively utilized in the generation of steam in accordance with the present invention.

While in accordance with the provisions of the statutes I have illustrated and described herein a preferred embodiment of the invention, those skilled in the art will understand that changes may be made in the method of operation and form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

l. The method of burning a low heat content gaseous fuel incapable of self-sustaining combustion in a vertically elongated cylindrical combustion zone which comprises introducing a plurality of streams of high heat value fluent fuel and combustion air into said combustion zone in vertically spaced substantially horizontal planes normal to the axis of said combustion zone, igniting and burning said fluent fuel to heat said combustion zone to a temperature in excess of the ignition temperature of said gaseous fuel, simultaneously introducing streams of said low heat content gaseous fuel having a high sensible heat into said comb stion zone in a direction normal to the axis of said zone and spaced axially between said planes of said introduced streams of high heat value fuel, igniting and burning said gaseous fuel in said combustion zone and regulating the amount of combustion air introduced with said high heat value fluent fuel to meet the .air requirements for the combustion of said low heat content gaseous fuel.

2. The method of burning a low heat content gaseous fuel incapable of self-sustaining combustion in a vertically elongated cylindrical combustion zone which comprises introducin' a plurality of circumf rentially equally spaced streams of heat value fuel and combustion air into said combustion zone in a common plane and tangent to a circle coaxial with the vertical axis of said combustion zone, simultaneously introducing streams of said low heat content gueous fuel having a high sensible heat into said combustion zone in a plane parallel to the plane of introduction of said high heat value fuel and spaced therefrom, staggering the introduced streams of high heat value fuel with respect to said streams of low heat content fuel, igniting and at least partially burning the high heat value fuel before said fuel streams mix in said combustion zone to heat said combustion zone above the ignition temperature of said low heat content fuel, and regulating the amount of combustion air introduced with said high heat value fluent fuel to meet the air requirernents for the combustion of both said high heat value and low heat content fuels.

3. Apparatus for burning low concentrations of carbon monoxide in large volumes of high velocity waste flue gases which comprises a vertically positioned circularly shaped combustion chamber, a plurality of means symmetrically disposed in each of a plurality of levels about said combustion chamber for injecting tangentially into said combustion chamber carbon monoxide in high velocity waste flue gases, means for supplying a forced draft to said combustion chamber to insure vertical movement of gases in said chamber, a plurality of means symmetrically disposed in each of a plurality of levels about said chamber for burning an auxiliary fuel and projecting the burning fuel into the combustion chamber substantially transversely to the horizontal path of injection of flue gases to said chamber, each of the plurality of levels of the auxiliary fuel injecting means being located irnmediately above each of the plurality of levels of the means provided for injecting flue gas, means to supply flue gases to the flue gas injecting means, means to supply fuel to the auxiliary fuel injecting means, means to supply air to the burner means and means to conduct gas from said combustion chamber to a heat recovery system.

4. A method for the recovery of heat of combustion of carbon monoxide which is present in low concentrations in large volumes of substantially inert high velocity waste flue gases Which comprises burning a fuel in the presence of an excess of air and projecting the resulting flaming fuel and excess air substantially horizontally across a vertically disposed circularly shaped combustion zone at a plurality of points disposed in a plurality of levels about said zone, tangentially passing a high velocity waste flue gas containing a low concentration of carbon monoxide substantially horizontally into the combustion zone and substantially transverse to the direction of flame projection at a plurality of points circumferentially disposed about said combustion zone in a plurality of vertically disposed levels, each of said levels for tangentially passing flue gas into said zone being immediately below each of the levels where flaming fuel passes into the zone, and raising the temperature of the flue gases to above about 1400 P. by passing the flue gases upwardly into direct contact with the flaming fuel whereby the carbon monoxide content of the flue gases spontaneously combines with the oxygen in the excess air to form carbon dioxide and release its heat of combustion and further raise the temperature of the gases, and passing the gases to a heat recovery system.

5. Apparatus for burning low concentrations of carbon monoxide in large volumes of high velocity Waste flue gases which comprises a vertically positioned circularly shaped combustion chamber, a plurality of means symmetrically disposed in the same level about said combustion chamber for injecting tangentially into said combustion chamber carbon monoxide in high velocity Waste flue gases, a plurality of means symmetrically disposed in the same level about said chamber for burning an auxiliary fuel and projecting the burning fuel into the combustion chamber substantially transversely to the horizontal path of injection of flue gases to said chamber, the level of the auxiliary fuel injecting means being located immediately above the level of the means provided for injecting flue gas, means to supply flue gases to the flue gas injecting means, means to supply fuel to the auxiliary fuel injecting means, means to supply air to the burner means and means to conduct gas from said combustion chamber to a heat recovery system.

6. A method for the recovery of heat of combustion of carbon monoxide which is present in low concentrations in large volumes of substantially inert high velocity Waste flue gases which comprises burning a fuel in the presence of an excess of air and projecting the resulting flaming fuel and excess air substantially horizontally across a vertically disposed circularly shaped combustion zone at a plurality of points disposed in the same level about said zone, tangentially passing a high velocity Waste flue gas containing a low concentration of carbon monoxide substantially horizontally into the combustion zone and substantially transverse to the direction of flame projection at a plurality of points circumferentially disposed about said combustion zone in the same level, said level for tangentiaily passing flue gas into said zone being immediately below the level Where flaming fuel passes into the zone, and raising the temperature of the flue gases to above about 1400 F. by passing the flue gases upwardly into direct cont-act with the flaming fuel whereby the carbon monoxide content of the flue gases spontaneously combines With the oxygen in the excess air to form carbon dioxide and release its heat of combustion and further raise the temperature of the gases, and passing the gases to a heat recovery system.

7. Apparatus for burning low concentrations of carbon monoxide in large volumes of high velocity waste flue gases which comprises a vertically positioned circularly shaped combustion chamber, a plurality of means symmetrically disposed in each of a plurality of levels about said combustion chamber for injecting tangentially into said combustion chamber carbon monoxide in high velocity waste flue gases, a plurality of means symmetrically disposed in the same level about said chamber for burning an auxiliary fuel and projecting the burning fuel into the combustion chamber substantially transversely to the horizontal path of injection of flue gases to said chamber, the level of the auxiliary fuel injecting means being located between said plurality of levels of the means provided for injecting flue gas, means to supply flue gases to the flue gas injecting means, means to supply fuel to the auxiliary fuel injecting means, means to supply air to the burner means and means to conduct gas from said combustion chamber to a heat recovery system.

8. A method for the recovery of heat of combustion of carbon 'monoxide which is present in low concentrations in large volumes of substantially inert high velocity waste flue gases which comprises burning a fuel in the presence of an excess of air and projecting the resulting flaming fuel and excess air substantially horizontally across a vertically disposed circularly shaped combustion zone at a plurality of points disposed in the same level about said zone, tangentially passing a high velocity waste fine gas containing a low concentration of carbon monoxide substantially horizontally into the combustion zone and substantially transverse to the direction of flame projection at a plurality of points circumferentially disposed about said combustion zone in a plurality of verticaly disposed levels, said levels for tangentially passing fine gas into said zone being immediately above and below respectively the level where flaming fuel passes into the zone, and raising the temperature of the line gases to above about 1400 F. by passing the flue gases into direct contact with the flaming fuel whereby the carbon monoxide content of the line gases spontaneously combines with the oxygen in the excess air to form carbon dioxide and release its heat of combustion and further raise the temperature of the gases, and passing the gases to a heat recovery system.

References Cited in the file of this patent UNITED STATES PATENTS 867,177 Welles Sept. 24, 1907 901,232 Eldred Oct. 13, 1908 1,441,721 Caracristi Jan. 9, 1923 1,969,501 Chapman Aug. 7, 1934 2,119,580 Hardgrove June 7, 1938 2,216,117 Krug Oct. 1, 1940 FOREIGN PATENTS 847,570 France July 3, 1939 697,840 Great Britain Sept. 30, 1953 698,939 Great Britain Oct. 28, 1953 OTHER REFERENCES 20 79 (pages 133, 134 and 135 relied upon. (Copy in Scientific Library.) 

1. THE METHOD OF BURNING A LOW HEAT CONTENT GASEOUS FUEL INCAPABLE OF SELF-SUSTAINING COMBUSTION IN A VERTICALLY ELONGATED CYLINDRICAL COMBUSTION ZONE WHICH COMPRISES INTRODUCING A PLURALITY OF STREAMS OF HIGH HEAT VALUE FLUENT FUEL AND COMBUSTION AIR INTO SAID COMBUSTION ZONE IN VERTICALLY SPACED SUBSTANTIALLY HORIZONTAL PLANES NORMAL TO THE AXIS OF SAID COMBUSTION ZONE, IGNITING AND BURNING SAID FLUENT FUEL TO THE IGNITION TEMPERATURE OF A TEMPERATURE IN EXCESS OF THE IGNITION TEMPERATURE OF SAID GASEOUS FUEL, SIMULTANEOUSLY INTRODUCING STREAMS OF SAID LOW HEAT CONTENT GASEOUS FUEL HAVING A HIGH SENSIBLE HEAT INTO SAID COMBUSTION ZONE IN A DIRECTION NORMAL TO THE AXIS OF SAID ZONE AND SPACED AXIALLY BETWEEN SAID PLANES OF SAID INTRODUCED STREAMS OF HIGH HEAT VALUE FUEL, IGNITING AND BURNING SAID GASEOUS FUEL IN SAID COMBUSTION ZONE AND REGULATING THE AMOUNT OF COMBUSTION AIR INTRODUCED WITH SAID HIGH HEAT VALUE FLUENT FUEL TO MEET THE AIR REQUIREMENTS FOR THE COMBUSTION OF SAID LOW HEAT CONTENT GASEOUS FUEL. 